1. Field of the Invention
The invention relates to an information carrier comprising a recording area for writing patterns representing user information, and a header area comprising patterns representing header information, the header area comprising a synchronization area having a predetermined synchronization pattern for synchronizing a clock frequency in a device in which the information carrier is used.
The invention also relates to a reading device for reproducing information from such an information carrier, and to a recording device for writing patterns representing user information onto such an information carrier.
In the context of this application, the term “marks” is to be understood to include all optically detectable regions on the information carrier, such as, for example, amorphous regions within a crystalline surrounding on an information carrier of the phase change type, or pits on an information carrier comprising embossed data, while the term “spaces” is to be understood to include all regions surrounding the marks. A pattern of marks and spaces represents the information on an information carrier.
2. Description of the Related Art
An information carrier according to the preamble is known from the European Computer Manufacturers Association Standard ECMA-154. Such an information carrier is also described in the Handbook of Magneto-Optical Data Recording; McDaniel, T W and Victora, R H; Noyes Publications; 1997. On the known information carrier, information is recorded in tracks, a track being formed by a 360 degree turn of a continuous spiral. Each track is sub-divided into a number of segments, each segment starting with a header area. The user information is written in the segment areas between the header areas.
The header areas comprise patterns representing header information. This header information is used in a reading device and in a recording device to correctly assess or record information on the information carrier. The header area comprises, for example, a pattern (i.e., the Address Mark) indicating that the patterns to follow represent the address of the segment. The header area also comprises a synchronization area, a so-called VFO field, for synchronizing a clock in the reading device and in the recording device in which the information carrier is used. Such a clock is, for example, generated by Variable Frequency Oscillator (VFO) circuitry located in the respective devices.
This VFO field is used to “lock up”, i.e., establish the proper frequency and phase of the read/write channel clock in the devices when the header is read. More specifically, the VFO field establishes the write channel clock frequency and phase when a segment is being written, and it establishes the read channel clock frequency and phase when a segment is being read. In general, this “lock up” is realized by Phase-Locked Loop (PLL) circuitry which relates the read/write channel clock to a signal obtained by reading the synchronization pattern in the VFO field.
The VFO field is also used to set the slicer level of circuitry which converts an analog High Frequency (HF) signal, obtained by reading the patterns of marks and spaces representing the information, into a digital information signal. Furthermore, the VFO field is used to set the dynamic range of an Automatic Gain Controlled (AGC) amplifier which ensures that the full range of analog-to-digital conversion circuitry is utilized.
The segment areas between the header areas also comprise a VFO field. The user information is preceded by a predetermined synchronization pattern, this pattern being used to set the dynamic range of an Automatic Gain Controlled (AGC) amplifier, to set the slicer level of circuitry which converts an analog High Frequency (HF) signal, obtained by reading the patterns of marks and spaces representing the information, into a digital information signal, and to set the proper frequency and phase of the read/write channel clock in the devices when the predetermined synchronization pattern is read. These settings may deviate from those resulting from the reading of the predetermined synchronization pattern in the headers. This is due to the disc making process where header information and user information are not necessarily written with the same frequency and phase.
The VFO field consists of a predetermined synchronization pattern of marks and spaces. The predetermined synchronization pattern of the known information carrier consists of a sequence of 3T marks and 3T spaces, where T represents one channel bit length. This pattern results in a sequence of the shortest possible marks and spaces allowed by a (2,k) Run Length Limited (RLL) code used to convert the information into patterns representing the information on the information carrier, such as, for example, the EFMplus code used on DVD discs. Because of these short marks and spaces, a signal obtained by reading the VFO field contains a single high frequency which results in a fast “lock up” of the read/write channel clock in the respective devices.
However, the predetermined synchronization pattern of the known information carrier has the problem that the setting of the Automatic Gain Controlled (AGC) amplifier is not optimal when a synchronization pattern consisting of sequences of 3T marks and 3T spaces is used.